1. Field of the Invention
The present invention relates to an offset rotary joint (slanted plane rotary joint) unit of a robot in which joints can be bent in a two-dimensional plane only with rotation mechanisms, and more particularly to an offset rotary joint unit equipped with a rotation correction mechanism.
2. Description of the Prior Art
A variety of joint mechanisms are used in industrial or entertainment robots. For example, the typically used hinge joint mechanisms composed of a rotary shaft and a bearing unit may be of a shaft drive system in which the bearing unit serves as a fixed shaft and the rotation of a rotary shaft is controlled, a bearing drive system in which the shaft is fixed and the bearing unit rotation is controlled, a link drive system, or a combination thereof. In the shaft drive system and bearing drive system, the entire load on the driven side should be supported and rotationally driven in the same direction as the rotation direction of the shaft rotary unit. Therefore, a large rotation torque is required and the systems are not suitable for a high-load operation. On the other hand, in the link mechanism drive system, a large axial moment was obtained and the system was suitable for a high-load operation. However, since a large link mechanism was required for an external tubular portion, the utilization of the external tubular portion as an arm mechanism of a robot failed to satisfy the requirements placed on the nursing assistant robots that require complex motions.
The inventors have previously suggested an arm-type multi-joint robot in which offset rotary joints are linked to each other as joints designed for a high load, this system being different from that of hinge joints (U.S. patent application Ser. No. 09/708,667). A specific feature of such a multi-joint robot is in that an end effect or can execute a complex motion and the positioning thereof is simple. However, the drawback of such a robot was that because an intermediate joint unit moved in a complex manner in a zigzag direction, the robot was unsuitable for simple motion such as bending in a two-dimensional plane. Furthermore, the motion range of the intermediate joint unit had to be determined in advance.
As described above, in the hinge-type joints of a shaft drive system or a bearing drive system, the inherent weight is received by a thin shaft, and because of the shaft control, a large load is applied to the bearings. Another drawback of such joints is that utilization conditions are degraded because of a structure in which a part of wiring, for example, of motors protrudes to the outside of a cylindrical body. On the other hand, since the offset rotary joints can be composed only of rotary mechanisms, a high load can be handled with comparatively small arms. However, the drawback of such joints is that because of a structure in which a bending angle with respect to a cylindrical body axis is set by conically rotating the shaft maintained at an offset angle (slant angle) with respect to the cylindrical body axis, the direction of bending angle in the intermediate positions cannot be determined. The resulting problem was that, for example, a simple two-dimensional bending motion was difficult to execute.